1. Field of the Invention
The present invention relates to a method of descaling surfaces having oscillation marks of cast billets, in particular of light-gage slabs, produced by a continuous casting process and reduced in a hot strip train including an equalizing furnace and, preferable, a plurality of rolling mill stands. The present invention also relates to an apparatus for effecting the method.
2. Description of the Prior Art
There exist certain difficulties in cleaning of surfaces of cast billets, in particular of light-gage slabs, produced by a continuous casting machine. These difficulties are primarily caused by the fact that the surfaces of the cast billets have irregularities, so-called, oscillation marks extending transverse to the displacement direction of the cast billets as they leave the continuous casting machine. These oscillation marks result from the oscillation of the metal mold.
These difficulties are enhanced by the fact that the oscillation marks do not remain constant during the casting operation. They vary during the casting operation and, in particular, their depth varies.
With time, in the course of improvement to the continuous casting technology, particular attention was devoted to the design and the function of the metal mold, and both, forming a centerpiece of a continuous strip casing technology, are constantly improved. Parallel therewith, an improved cast powder was tested and used as a lubricant, contributing to an increase of casting speeds.
The use of a high-frequency oscillation system in connection with an optimal geometry of the metal mold permitted to achieve a constant improvement of the surface quality of the cast products.
Despite this noticeable improvement of the surface quality, there still exists a need, in particular for light-gage slabs, to clean the cast products from impurities, such as dust particles, foreign particles clinging to the surfaces, etc. . . . by descaling in order to prevent their rolling in the surfaces of the cast products during the rolling of the cast product in rolling mill stands. In particular, these impurities should be removed from the bottoms of still existing oscillation marks which is particularly difficult when the oscillation marks have an angular or pointed cross-section.
Accordingly, an object of the present invention is a method and an apparatus which would permit to overcome the difficulties encountered during cleaning of the surfaces of continuously cast products, in particular light-gage slabs, and more particularly, which would permit to remove impurities containing in and around the oscillation marks.
Another object of the present invention is to provide a method of and an apparatus for descaling surfaces of the cast products which would prevent an undesired excessive cooling of the cast product by using as little amount of water under pressure as possible.
These and other objects of the present invention, which will become apparent hereinafter, are achieved, according to the present invention, by subjecting surfaces of a cast billet, in a limited region between an end of the billet guide and an entrance of the equalizing furnace or a first rolling mill stand, by at least a double deflection of the cast billet from a horizontal transporting path of the cast billet, to stretching in a region of each deflection, and by subjecting the surfaces of the cast billet to an intensive flushing with hard water jets in the deflection regions of the light-gage slab.
The contemplated, according to the present invention, deformation of the cast billet permits to provide tensile stress regions which insure a somewhat wider opening of the oscillation marks which, in turn, insure a better action of the hard water jets, providing for a more intensive cleaning effect penetrating up to the bottoms of the oscillation marks.
According to a preferred embodiment of the present invention, the cast billet is deflected sinusoidally or approximately sinusoidally.
The sinusoidal or approximately sinusoidal deflection insures an approximately uniform increase and decrease of the surface stress, preventing damage of the cast billet structure.
Accordingly, to a further development of the present invention, an amount of each deflection of the cast billet is determined in accordance with a maximum allowable deformation of the cast billet and/or a maximum allowable surface tension of the cast billet.
Accordingly, to a still further development of the present invention, an amount of each deflection is determined in accordance with a temperature of the cast billet under a condition of a permanent temperature control.
The maintenance of allowable deformation, maximum allowable surface tension or temperature insures a maximum bending of the cast billet, while preventing any damaging structural changes in the cast billet.
According to the present invention, the distance between the spray nozzles and the flushed surfaces is continuously measured and adjusted so that this distance remains substantially constant. This permits to maintain the operational parameters of the hard cleaning jets of water constant to a most possible extent.
To this end, it is contemplated to constantly measure the pressure of the spray water and to maintain the water pressure at a high level.
According to a further preferred embodiment of the present invention, it is contemplated to impinge respective surfaces with a plurality of water jets lying in parallel planes and arranged in a row, with the planes of the water jets extending at an angle to a respective plane extending transverse to a transporting direction of the cast billet, and with the water jets being inclined to respective surfaces of the cast billet.
The advantage of directing of water jets in the foregoing manner insures that the pressure water jets can more easily reach the bottoms of the oscillation marks. This is because a transverse or inclined infringement direction of the water jets with respect to the displacement direction of the cast billet proved to be more favorable for cleaning purposes than a parallel direction.
A further improvement of the cleaning action is achieved by reciprocating girders with water jet-producing nozzles in planes extending transverse to the transporting or displacement direction of the cast slab.
According to yet another embodiment of the present invention, a variable deflection force in accordance with a structural condition of the cast billet corresponding to cooling, which takes place simultaneously with the descaling, is measured, and the water consumption is constantly adjusted, with maintaining a product of the water amount and the water pressure constant. Thereby, it becomes possible to compensate changes in the billet parameters which occasionally can be caused by the operation of the continuous casting machine, e.g., as a result of a change of the casting speed or the casting temperature.
An apparatus for descaling surfaces having oscillation marks of cast billets produced by a continuous casting process and reduced in a hot strip train including an equalizing furnace and a plurality of rolling mill stands, with the cast billets being delivered from a continuous casting machine through a billet guide, includes a pair of straightening guide rollers provided at and end of the billet guide, a pair of bending drive rollers provided in front of an entrance of the equalizing furnace or an entrance of the rolling mill stands, and a descaling station arranged between the pairs of the straightening drive rollers and the bending drive rollers and including at least two oppositely arranged deflection bending rollers spaced from each other in a transporting direction, and a spray girder provided on each of opposite sides of the cast billet and having a plurality of spray nozzles arranged in an inclined plane.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.